The present invention relates to polymer moulding technology and apparatus, and more particularly to a polymer's electromagnetic dynamic injection moulding method and the apparatus therefor.
The plasticating injection device of the most commonly used conventional injection molding machine is the screw in-line injection device which is a modification of the conventional screw extruder. This kind of injection device is different from the extruder in that when the materials are being plasticized, the screw retreats and the molten materials are being charged into the space in the charging barrel created by the retreat of the end of the screw. When a certain quantity of molten materials is reached, the screw acting as a piston is made to advance by external force to inject the materials from the charging barrel into the mould cavity communicated therewith. This type of injection device has three deficiencies as follows:
(1) Owing to the retreat of the screw during plasticating, the effective length of the plasticating device is shortened, so that the effect of plasticating and mix of the molten material is not homogeneous and there is temperature difference and nonhomogeneity of temperature distribution for the molten material in the charging barrel both radially and axially affecting the quality of the products after injection.
(2) During the injection, the screw moves in segmental uniform velocity, causing the molten material to fill the mould cavity with sectioned, stable pressure, so that the viscosity and elasticity of the melt are greater, and so is the resistance to fill the mould cavity. The difficulty of filling and compacting is subject to insufficiency of filling and retaining of inner stress in the product.
(3) The high temperature needed to plasticize the materials in a conventional plasticization injection device causes the temperature of the molten material to be also high, thus causing the time for cooling the moulded products prolonged and likewise for the moulding cycle of the product.
Chinese patent NO. 90101034.0 &lt;Electromagnetic Dynamic Plasticization Extruding Method and the Equipment Therefor&gt; and Chinese patent NO. 92103639.6 &lt;Screw In-line Electromagnetic Dynamic Extruder&gt; disclosed an electromagnetic dynamic plasticization extruder quite different from the conventional screw extruder. In this extruder, the oscillating field has been indroduced into the overall process of the plasticating extrusion of polymers, altering the way of energy transduction, structural form and way of plasticating extrusion of the conventional extrution equipments creating an integrating dynamic plasticating extruder in which mechanic, electronic and electromagnetic technologies are combined into one. This sort of extruder substantially overcomes the shortcomings of the conventional extruder and has many advantages that the conventional extruder fails to have. If the design concept of this electromagnetic dynamic plasticating extruder is used to modify the plasticization injecting device of the injection machine, it will be possible to make the injection machine to have the same or similar characteristics and advantages. Further, if the oscillating field is introduced at the same time into the processes of metering and filling the mould by injection, the above-mentioned deficiencies of the conventional injection device will be completely overcome.